Zoom lens

ABSTRACT

In this invention, to provide a compact zoom lens having a small number of optical element groups to be driven and a simple moving mechanism, at least one of a plurality of optical element groups arranged in the lens system includes a refractive power variable element of a transmission type which has a compensation function to correct focus movement caused by zooming and a focus function to correct focus movement caused by a variation in inter-object distance. The refractive power variable element is a liquid optical element including a first liquid having a conductivity or a polarity and a second liquid which is not mixed with the first liquid, the first liquid and the second liquid being enclosed in a container fluid-tight so as to define an interface therebetween having a predetermined shape, the liquid optical element being arranged such that a refractive power thereof is adjusted by changing a curvature of the interface.

This application is based on and claims priority under 35 U.S.C. §119from the Japanese Patent Applications Nos. 2004-070398, 2004-070399 and2004-259533 filed in Japan on Mar. 12, 2004, Mar. 12, 2004 and Sep. 7,2004, respectively, at least respective entire contents of which areincorporated herein by reference.

TECHNOLOGICAL FIELD

The present invention relates to a zoom lens and, more particularly, tocompact zoom lens used in a solid-state image sensing element such as aCCD image sensor or CMOS image sensor.

TECHNOLOGICAL BACKGROUND

In recent years, as image sensing apparatuses using a solid-state imagesensing element such as a CCD (Charge Coupled Device) image sensor orCMOS (Complementary Metal Oxide Semiconductor) image sensor increasetheir performance and reduce the size, cellular phones and PDA (PersonalDigital Assistances) with a subminiature digital camera or image sensingapparatus are becoming popular. In addition, demand to mount a zoom lensin these image sensing apparatuses is growing.

In a general zoom lens, all or some of lens groups included in the imagesensing lens must be moved. In, e.g., a 3-group zoom lens, lens groupsare divided into three groups: a variator group which changes the focallength, a compensator group which corrects focus movement caused by thechange in focal length, and a focus group which corrects focus movementcaused by the change in object distance, or a variator group, a grouphaving a compensator and focus function, and a fixed group. Of the lensgroups, predetermined lens groups are moved in the coaxial direction toexecute zooming and focus adjustment. As a detailed example of such azoom optical system, a zoom lens which executes zooming and focusadjustment by moving two or three groups is disclosed (JapaneseUnexamined Patent Publication No. 2002-350726).

As disclosed in Unexamined Patent Publication No. 2002-350726, when aplurality of lens groups are moved in the coaxial direction to executezooming and focus adjustment, a moving mechanism to move the lens groupsis necessary. The moving mechanism is generally complex. In addition, awide space is necessary to arrange the moving mechanism.

Another zoom lens is known, which decreases the number of moving groupsby using a refractive power variable element and imparts, to thiselement, the focus movement correction function for zooming or avariation in inter-object distance. As a detailed example of such a zoomlens, a zoom lens using a reflection refractive power variable elementis also disclosed (Japanese Unexamined Patent Publication No.2003-98435).

However, when the reflection optical element disclosed in JapaneseUnexamined Patent Publication No. 2003-98435 is used, aberrationasymmetrical with respect to the co-axis is generated. To correct theaberration, the reflecting surface must be, e.g., a free-form surfacewhich is hard to control.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the aboveproblems of the prior arts, and has as its object to provide a compactzoom lens which includes a small number of drive lens groups and asimple moving mechanism by causing at least one of lens groups eachhaving a plurality of lenses to include a refractive power variableelement of a transmission type.

It is another object of the present invention to provide a zoom lenswhich has an excellent maximum transmittance by making use of a liquidoptical element and its drive means.

In order to achieve the above objects, according to a first aspect ofthe present invention, there is provided a zoom lens in which aplurality of optical element groups including at least an opticalelement group which moves in zooming are arranged in a lens system,comprising: a refractive power variable element of a transmission typewhich is mounted in at least one of the plurality of optical elementgroups, the refractive power variable element having a compensationfunction to correct focus movement caused by zooming and a focusfunction to correct focus movement caused by a variation in inter-objectdistance.

The optical system including the optical element group which movesduring zooming includes the refractive power variable element which hasthe compensation function to correct focus movement caused by zoomingand the focus function to correct focus movement caused by a variationin inter-object distance. With this structure, the moving amount of theoptical element group which moves for compensation and focusing can besuppressed small. Alternatively, the optical element group whichrequires a mechanical driving mechanism can be only the zooming group.Hence, a compact zoom lens having a small number of optical elementgroups to be driven and a simple moving mechanism can be implemented.

According to a second aspect of the present invention, there is provideda zoom lens in which a plurality of optical element group including atleast an optical element group which moves in zooming are arranged in alens system, comprising: at least a refractive power variable element ofa transmission type provided in the plurality of optical element groups;an electromechanical conversion element which is extendible/contractibleby applying thereto a drive voltage in the form of predetermined pulses;a drive member fixed to one end of the electro-mechanical conversionelement; a movable member coupled to the optical element group andmovably mounted on the drive member; and a drive means for moving themovable member through repetitions of extension and contraction of theelectromechanical conversion element at different speeds in directionsof extension and contraction which is caused by applying the drivevoltage in the form of the predetermined pulses to the electromechanicalconversion element.

In the above-mentioned drive means, by applying a drive voltage in theform of, for example, pulses each having a saw-toothed shape to theelectromechanical conversion element for an extreme short time, theelectromechanical conversion element can be deformed so as to beslightly expanded or contracted, and further, the speeds of extensionsand contractions can be changed in accordance with a waveform of thepulses. At this stage, when the electromechanical conversion element isdeformed in a direction of extension or contraction at a high speed, themovable member does not follow the motion of the drive member but staysat a position as it is due to its mass inertia. Meanwhile, when theelectromechanical element is deformed at a slower speed in a reversedirection, the movable member is moved following the motion of the drivemember due to a friction effecting therebetween. Thus, due torepetitions of extension and contraction of the electromechanicalconversion element, the movable member can be continuously moved in onedirection. That is, with the use of the drive means according to thepresent invention, having a high responsiveness, the optical elementgroups which are moved upon zooming can be moved at a high speed, andcan be also moved by a slight displacement. Further, in such a case thatthe optical element groups which are moved upon zooming, are held inposition, when the supply of an electric power to the electromechanicalconversion element is interrupted, they are held by a friction forcebetween the movable member and the drive member, thereby it is possibleto aim at saving energy. In addition, it can offer such an advantagethat the configuration of the drive means can be simplified, and can beat a low cost.

According to a third aspect of the present invention, there is provideda zoom lens according to the first aspect, wherein a refractive power ofthe optical element group including the refractive power variableelement of a transmission type has an extremum during zooming.

When the refractive power of the optical element group including therefractive power variable element has an extremum during zooming, thechange in refractive power of the refractive power variable element canbe made small during zooming. Hence, the refractive power variableelement can be easily controlled.

According to a fourth aspect of the present invention, there is provideda zoom lens according to one of the first to third aspects, wherein therefractive power is changed by changing a radius of curvature of anoptical surface at which the refractive power variable element contactsair.

According to a fifth aspect of the present invention, there is provideda zoom lens according to any one of the first to third aspects, whereinthe refractive power is changed by changing a refractive index of anoptical material of the optical element.

When the refractive power is changed by changing the radius of curvatureof the optical surface at which the refractive power variable elementcontacts air, the absolute value of the refractive power of theinterface between the optical surface and the medium in contact theoptical surface is large as compared to a case in which the medium whichcontacts the optical surface is not air. In other words, if theinterface has the same absolute value of the refractive power, therefractive power variable element whose optical surface contacts air canincrease the absolute value of the radius of curvature of the opticalsurface as compared to a refractive power variable element whose opticalsurface contacts a medium except air. For this reason, aberrationgenerated on the interface can be reduced. When the refractive power ischanged by changing the refractive index of the optical material of theoptical element, the variation in higher order aberration in changingthe refractive power can be made small as compared to the refractivepower variable element which changes the refractive power by changingthe shape of the optical element surface.

According to a sixth aspect of the present invention, there is provideda zoom lens according to any one of the first to fifth aspects, whereinonly one optical element group moves in zooming.

When only one optical element group moves in zooming, a zoom lens havinga small number of optical element groups to be driven and a simplemoving mechanism can be implemented.

According to a seventh aspect of the present invention, there isprovided a zoom lens according to any one of the first to sixth aspects,wherein a position of the optical element group including the refractivepower variable element is fixed in a direction of an optical axis.

When the position of the optical element group including the refractivepower variable element is fixed in the direction of the optical axis,the moving mechanism including the wiring of a flexible cable for theliquid optical element can be more simple as compared to a case in whichthe optical element group including the liquid optical element moves.

According to an eighth aspect of the present invention, there isprovided a zoom lens according to the first aspect, wherein the zoomlens comprises a refractive power variable element of a transmissiontype mounted in an optical element group which moves in zooming, therefractive power variable element having a compensation function tocorrect focus movement caused by zooming, a focus function to correctfocus movement caused by a variation in inter-object distance, and azooming function.

In the optical system including the optical element group which movesduring zooming, the optical element group which moves in zoomingincludes the refractive power variable element and has the compensationfunction to correct focus movement caused by zooming, focus function tocorrect focus movement caused by a variation in inter-object distance,and zooming function. With this structure, the moving amount of thezooming group in zooming or the moving amount of the moving opticalelement group to correct focus movement caused by a variation ininter-object distance can be suppressed small. Alternatively, theoptical element group which requires a mechanical driving mechanism canbe only the zooming group. Hence, a compact zoom lens having a smallnumber of optical element groups to be driven and a simple movingmechanism while suppressing the moving amount of the moving opticalelement group small can be implemented. Having a zooming functionindicates that the absolute value of the refractive power of the groupincluding the liquid optical element serving as the zooming group islarger at the long focal length end than at the short focal length end.

According to a ninth aspect of the present invention, there is provideda zoom lens according to any one of the first to eighth aspects, whereinthe optical element group including the refractive power variableelement includes a diaphragm.

When the optical element group, which includes the refractive powervariable element, includes a diaphragm, the diameter of the refractivepower variable element can be made small, and a compact zoom lens can beimplemented.

According to a 10th aspect of the present invention, there is provided azoom lens according to the first aspect, wherein the refractive powervariable element of a transmission type comprises a liquid opticalelement including a first liquid having a conductivity or a polarity anda second liquid which is not mixed with the first liquid, the firstliquid and the second liquid being enclosed in a container fluid-tightso as to define an interface therebetween having a predetermined shape,the liquid optical element being arranged such that a refractive powerthereof is adjusted by changing a curvature of the interface.

With the use of the liquid optical element as an component, since thecurvature of the interface is changed so as to adjust the refractivepower, a compensation operation for correcting a focus movement causedby zooming, and a focus function for correcting a focus movement causedby a variation in an object distance can be materialized, thedisplacement of the optical element group adapted to move for thecompensation and the focusing can be restrained to a small value, andthe optical element groups which require a mechanical drive mechanismcan be limited to those for zooming, thereby it is possible to provide asmall-sized zoom lens having a less number of optical element groupswhich have to be moved and having a simple mechanical system. Inparticular, the above-mentioned liquid type optical element issubstantially transparent and has an excellent maximum transmittance.

According to an 11th aspect of the present invention, there is provideda zoom lens according to the 10^(th) aspect, wherein the liquid opticalelement is arranged in an optical element group which includes adiaphragm. With this configuration, the outer diameter of the liquidoptical element can be decreased, thereby it is possible to provide asmall-size zoom lens.

According to a 12th aspect of the present invention, there is provided azoom lens according to the 10^(th) aspect, wherein in the case of anoptical element group which does not include a diaphragm but the liquidoptical element, the liquid optical element is arranged at a positionneared to the diaphragm. With this configuration, the outer diameter ofthe liquid optical element can be decreased.

According to a 13th aspect of the present invention, there is provided azoom lens according to any one the 10th, 11th and 12th aspects, whereinone of the optical element groups is moved upon zooming. Thereby it ispossible to a zoom lens having a less number of optical element groupsto be moved, and having a simple mechanical system.

According to a 14th aspect of the present invention, there is provided azoom lens according to any one of the 10^(th) and 11th to 13th aspects,wherein the optical element group including the liquid optical elementis fixed in the direction of the optical axis, and the optical elementgroup including the liquid optical element has a compensation functionfor correcting a focus movement caused by zooming and a focus functionfor correcting a focus movement caused by a variation in objectdistance.

With this configuration in which the optical element group including theliquid optical lens is fixed in the direction of the optical axis, andperforms the compensation function for correcting a focus movementcaused by zooming and a focus function for correcting a focus movementcaused by a variation in object distance, the displacement of theoptical element groups to be moved can be suppressed to a small value,and the optical element groups which require a mechanical operatingmechanism can be limited to those for zooming, thereby it is possible toprovide a zoom lens having a less number of optical element groups to bedriven and a simple mechanical configuration in which the wiring offlexible cables and the like for the liquid optical element can besimplified in comparison with a zoom lens in which the optical elementgroup including the liquid optical element is moved.

According to a 15th aspect of the present invention, there is provided azoon lens according to the second aspect, wherein each of the pluses hasa saw-toothed shape.

According to a 16th aspect of the present invention, there is provided acamera comprises a zoom lens having at least an optical element groupprovided in a plurality of optical element groups arranged in a lenssystem, the optical element group being made to move in zooming, and atleast a refractive power variable element of a transmission type havinga compensation function to correct focus movement caused by zooming anda focus function to correct focus movement caused by a variation ininter-object distance.

As is clearly understood from the foregoing aspects, according to thepresent invention, at least one of lens systems including a plurality oflenses includes the refractive power variable element of a transmissiontype. With this structure, a compact zoom lens having a small number ofoptical element groups to be driven and a simple moving mechanism can beprovided.

The above and many other features, objects and advantages of the presentinvention will become manifest to those skilled in the art upon makingreference to the following detailed description and accompanyingdrawings in which preferred embodiments incorporating the principle ofthe present invention are shown by way of illustrative examples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic views of a zoom lens according to thefirst embodiment of the present invention;

FIGS. 2A and 2B are schematic views of a zoom lens according to thesecond embodiment of the present invention;

FIG. 3 is a schematic view showing an example of a refractive powervariable element which can suitably be used in the zoom lens accordingto the embodiment of the present invention;

FIG. 4 is a graph showing the relationship between the refractive power(ordinate) and focal length (abscissa) in the zoom lens according to thepresent invention;

FIGS. 5A to 5C are sectional views illustrating a zoom lens in a firstembodiment of the present invention;

FIG. 6 is a schematic sectional view illustrating a liquid opticalelement QL and a drive part thereof;

FIG. 7A to 7C are sectional views illustrating a zoom lens in a secondembodiment of the present invention;

FIGS. 8A to 8C are views which show aberrations of the zoom lens in thefirst embodiment of the present invention;

FIG. 9A to 9C are views which show aberrations of the zoom lenses in thefirst embodiment;

FIG. 10 is a perspective view illustrating a zoom lens unit ZU in whicha zoom lens in the above-mentioned embodiments and a drive meanstherefor are incorporated, integral with each other;

FIG. 11 is a perspective view illustrating a lamination typepiezoelectric actuator PZ having a structure in which a plurality ofpiezoelectric ceramics PE are laminated one upon another, and electrodesC interposed therebetween are connected in parallel; and

FIGS. 12A and 12B are views which show waveforms of voltage pulsesapplied to the piezoelectric actuator PZ.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described belowwith reference to the accompanying drawings.

FIGS. 1A and 1B are schematic views of a zoom lens according to thefirst embodiment of the present invention. FIG. 1A shows the short focallength end, and FIG. 1B shows the long focal length end. Since they aresimple illustrations, the lenses do not correspond to actual opticalsurface shapes. The zoom lens according to the first embodiment has lensgroups G1 to G3 to form an object image on an image sensing element CCD.The first lens group G1 is a refractive power variable element which isfixed to a mirror frame (not shown). The second lens group G2 includesnormal lenses integrated with a diaphragm S and can be moved in thedirection of the optical axis by a driving source (not shown). The thirdlens group G3 includes normal lenses and is fixed to a mirror frame (notshown). The third lens group G3 is not always essential.

FIG. 3 is a schematic view showing the refractive power variable elementG1 which can be applied to the zoom lenses according to the firstembodiment. The refractive power variable element G1 shown in FIG. 3 canchange the lens surface and accordingly the refractive power by causinga micropump MP to flow a fluid F in and out. The micropump MP is a smallpump formed by, e.g., micromachining and can be driven by a signal froma controller C shown in FIGS. 1A and 1B. The fluid F is stored between atransparent substrate TP1 and an elastic body EM. Referring to FIG. 3, atransparent substrate TP2 to protect the elastic body EM can be omitted.Other examples of a pump formed by micromachining are a pump usingthermal deformation, a pump using a piezoelectric material, and a pumpusing static electricity.

The operation of the zoom lens according to the first embodiment will bedescribed. When zoom driving is executed from the short focal length endto the long focal length end, the second lens group G2 is driven in thedirection of the optical axis from the position shown in FIG. 1A to theposition shown in FIG. 1B, as shown in FIGS. 1A and 1B. In zoom drivingfrom the long focal length end to the short focal length end, a reverseoperation is performed.

According to a conventional zoom lens, as the second lens group G2 movesin the direction of the optical axis, the first lens group G1 must bemoved in the direction of the optical axis to obtain the compensationfunction. To move the first lens group G1 in the direction of theoptical axis, a cam mechanism or the like must be prepared. This resultsin a complex structure or an increase in size of the image sensingapparatus in which the zoom lens is mounted.

Contrarily, in the zoom lens of the first embodiment, the controller Cchanges the shape of an optical surface S1 of the first lens group G1 asthe second lens group G2 moves in the direction of the optical axis.Hence, the compensation function can be implemented by using the changein refractive power. No mechanism to move the first lens group G1 in thedirection of the optical axis is necessary so that the structure can besimple and compact.

In the conventional zoom lens, the moving amount of the second lensgroup G2 in the direction of the optical axis and that of the first lensgroup G1 in the direction of the optical axis are in a one-to-onecorrespondence because of the cam shape. In actual image sensing, theobject distance changes. To obtain an in-focus state on thelight-receiving surface of the image sensing element CCD in accordancewith the object distance, a so-called focusing function is implementedby, e.g., displacing the third lens group G3 in the direction of theoptical axis. In this case, another driving mechanism must separately beprepared for the third lens group G3, resulting in a complex and bulkystructure.

In the zoom lens according to the first embodiment, however, thecontroller C can change the shape of the optical surface S1 of the firstlens group G1 on the basis of the zoom signal (or the moving amount ofthe second lens group G2 in the direction of the optical axis) and thesignal from the image sensing element CCD or the distance measurementsignal from a distance measuring device (not shown) so that thecompensation function and focusing function can be implementedsimultaneously. In this case, the third lens group G3 need not bedisplaced in the direction of the optical axis. When the refractivepower of the first lens group G1 including the refractive power variableelement has an extremum during zooming, the change in refractive powerof the first lens group G1 can be made small during zooming. Hence, thecontroller C can easily control the refractive power variable element.

To “have an extremum” will be described. For example, assume a zoom lenshaving a 3-group structure including a first lens group having anegative refractive power, a second lens group having a positiverefractive power, and a third lens group having a positive refractivepower. The first lens group is a fixed group including a refractivepower variable element. The second lens group is a zooming group whichmoves in zooming. The third lens group is a fixed group. To correctfocus movement caused by zooming, a refractive power P (G1) of the firstlens group takes an extremum, at which the absolute value of therefractive power is maximum, and then becomes small gradually as thefocal length of the zoom lens increases, as shown in FIG. 4. When thezoom lens is formed in the range where the refractive power of the firstlens group has the extremum, the change in refractive power of therefractive power variable element can be made as small as possible.

FIGS. 2A and 2B are schematic views of a zoom lens according to thesecond embodiment of the present invention. FIG. 2A shows the shortfocal length end, and FIG. 2B shows the long focal length end. Sincethey are simple illustrations, the lenses do not correspond to actualoptical surface shapes. The zoom lens according to the second embodimenthas lens groups G1 to G3 to form an object image on an image sensingelement CCD. The first lens group G1 includes normal lenses and is fixedto a mirror frame (not shown). The second lens group G2 is a refractivepower variable element integrated with a diaphragm S and can be moved inthe direction of the optical axis by a driving source (not shown). Thethird lens group G3 includes normal lenses and is fixed to a mirrorframe (not shown). The third lens group G3 is not always essential.

The second lens group G2 is supported by a mirror frame (not shown) andcomprises a hollow member which stores a liquid or gas inside and has anoptical surface S2 made of a transparent flexible film. Like therefractive power variable element shown in FIG. 3, the internal pressureof the second lens group G2 can be adjusted by an external controller C.The shape of the optical surface S2, i.e., the refractive power can bechanged by changing the internal pressure.

The operation of the zoom lens according to the second embodiment willbe described. When zoom driving is executed from the short focal lengthend to the long focal length end, the second lens group G2 is driven inthe direction of the optical axis from the position shown in FIG. 2A tothe position shown in FIG. 2B, as shown in FIGS. 2A and 2B. In zoomdriving from the long focal length end to the short focal length end, areverse operation is performed.

In the zoom lens according to the second embodiment, the controller Cchanges the shape of the optical surface S2 of the second lens group G2as it moves in the direction of the optical axis. Hence, thecompensation function can be implemented by using the change inrefractive power. No mechanism to move the first lens group G1 in thedirection of the optical axis is necessary so that the structure can besimple and compact.

Further, in the zoom lens according to the second embodiment, thecontroller C can change the shape of the optical surface S2 of thesecond lens group G2 on the basis of the zoom signal (or the movingamount of the second lens group G2 in the direction of the optical axis)and the signal from the image sensing element CCD or the distancemeasurement signal from a distance measuring device (not shown) so thatthe compensation function and focusing function can be implementedsimultaneously. In this case, the third lens group G3 need not bedisplaced in the direction of the optical axis. When the refractivepower of the optical element group including the second lens group G2has an extremum during zooming, the change in refractive power of thesecond lens group G2 can be made small during zooming. Hence, thecontroller C can easily control the refractive power variable element.

In the first and second embodiments, when the refractive power variableelement has a perfect zooming function, all lens groups can be fixed inthe direction of the optical axis so that a zoom lens having no lensgroup driving mechanism can also be implemented.

Exemplified embodiments of the zoom lens of the present invention willbe described below. Symbols used in Exemplified embodiments are asfollows.

-   -   P1(W), P1(M), and P1(T): the refractive powers of the first lens        at the short, intermediate, and long focal length ends    -   HF1(W), HF1(M), and HF1(T): the distances from the near-side        principal point of the first lens group to the surface apex of        the first lens group closest to the object at the short,        intermediate, and long focal length ends    -   HR1(W), HR1(M), and HR1(T): the distances from the far-side        principal point of the first lens group to the surface apex of        the first lens group closest to the image at the short,        intermediate, and long focal length ends    -   HD1(W), HD1(M), and HD1(T): the distances from the near-side        principal point to the far-side principal point of the first        lens group at the short, intermediate, and long focal length        ends    -   D1(W), D1(M), and D1(T): the distances from the surface apex of        the first lens group closest to the image to the surface apex of        the second lens group closest to the object at the short,        intermediate, and long focal length ends    -   P2(W), P2(M), and P2(T): the refractive powers of the second        lens at the short, intermediate, and long focal length ends    -   HF2(W), HF2(M), and HF2(T): the distances from the near-side        principal point of the second lens group to the surface apex of        the second lens group closest to the object at the short,        intermediate, and long focal length ends    -   HR2(W), HR2(M), and HR2(T): the distances from the far-side        principal point of the second lens group to the surface apex of        the second lens group closest to the image at the short,        intermediate, and long focal length ends    -   HD2(W), HD2(M), and HD2(T): the distances from the near-side        principal point to the far-side principal point of the second        lens group at the short, intermediate, and long focal length        ends    -   D2(W), D2(M), and D2(T): the distances from the surface apex of        the second lens group closest to the image to the surface apex        of the third lens group closest to the object at the short,        intermediate, and long focal length ends    -   P3(W), P3(M), and P3(T): the refractive powers of the third lens        at the short, intermediate, and long focal length ends    -   HF3(W), HF3(M), and HF3(T): the distances from the near-side        principal point of the third lens group to the surface apex of        the third lens group closest to the object at the short,        intermediate, and long focal length ends    -   HR3(W), HR3(M), and HR3(T): the distances from the far-side        principal point of the third lens group to the surface apex of        the third lens group closest to the image at the short,        intermediate, and long focal length ends    -   HD3(W), HD3(M), and HD3(T): the distances from the near-side        principal point to the far-side principal point of the third        lens group at the short, intermediate, and long focal length        ends    -   D3(W), D3(M), and D3(T): the distances from the surface apex of        the third lens group closest to the image to the image surface        at the short, intermediate, and long focal length ends    -   f(W), f(M), and f(T): the focal lengths of the zoom lens at the        short, intermediate, and long focal length ends    -   L(W), L(M), and L(T): the total lengths of the zoom lens at the        short, intermediate, and long focal length ends

Exemplified Embodiment 1

Exemplified embodiment 1 to be described below corresponds to the zoomlens according to the above-described first embodiment.

More specifically, the focal lengths, principal points, and principalpoint intervals of the respective groups, the group intervals, the focallength of the entire system, and the total length at object distance T=∞of the zoom lens are shown in Table 1. The focal lengths, principalpoints, and principal point intervals of the first lens group serving asa refractive power variable element at the short and long focal lengthends at object distance T=250 mm are shown in Table 2. The objectdistance indicates the distance from the object to the surface apex ofthe zoom lens closest to the object. For HF, HR, and HD in the tables,the direction from the object to the image is defined as positive. TABLE1 (Short Focal Length End: W) T = ∞ First Group P1 (W) = −0.082 HF1 (W)= 0.596 HR1 (W) = 5.707 HD1 (W) = 1.198 D1 (W) = 9.254 Second Group P2(W) = 0.114 HF2 (W) = 4.489 HR2 (W) = 4.767 HD2 (W) = 4.238 D2 (W) =1.500 Third Group P3 (W) = 0.086 HF3 (W) = 0.228 HR3 (W) = 2.319 HD3 (W)= 1.181 D3 (W) = 2.526 Overall System f (W) = 4.450 L (W) = 27.379(Intermediate Focal Length End: M) T = ∞ First Group P1 (M) = −0.092 HF1(M) = 0.245 HR1 (M) = 5.228 HD1 (M) = 1.327 D1 (M) = 4.779 Second GroupP2 (M) = 0.114 HF2 (M) = 4.489 HR2 (M) = 4.767 HD2 (M) = 4.238 D2 (M) =5.975 Third Group P3 (M) = 0.086 HF3 (M) = 0.228 HR3 (M) = 2.319 HD3 (M)= 1.181 D3 (M) = 2.526 Overall System f (M) = 7.224 L (M) = 27.379 (LongFocal Length End: T) T = ∞ First Group P1 (T) = −0.082 HF1 (T) = 0.596HR1 (T) = 5.707 HD1 (T) = 1.198 D1 (T) = 0.953 Second Group P2 (T) =0.114 HF2 (T) = 4.489 HR2 (T) = 4.767 HD2 (T) = 4.238 D2 (T) = 9.801Third Group P3 (T) = 0.086 HF3 (T) = 0.228 HR3 (T) = 2.319 HD3 (T) =1.181 D3 (T) = 2.526 Overall System f (T) = 11.109 L (T) = 27.379

TABLE 2 (Short Focal Length End: W)   T = 250 mm First Group P1(W) =−0.079 HF1(W) = 0.716 HR1(W) = 5.875 HD1(W) = 1.152 (Long Focal LengthEnd: T)   T = 250 mm First Group P1(T) = −0.089 HF1(T) = 0.342 HR1(T) =5.364 HD1(T) = 1.288

As shown in Table 1, when the focal length is changed from the shortfocal length end to the long focal length end, and the refractive powerof the first lens group G1 is changed simultaneously, compensation tocorrect focus movement caused by zooming is executed. In addition, asshown in Table 2, focusing can also be executed by changing therefractive power of the refractive power variable element as the objectdistance changes. For this reason, lens groups other than the secondlens group G2 serving as an optical element group having a zoomingfunction can be fixed. Hence, a zoom lens having a small number of drivelens groups and a simple moving mechanism can be implemented.

When the refractive power of the refractive power variable element hasan extremum during zooming to change the focal length from the shortfocal length end to the long focal length end, the change in refractivepower of the refractive power variable element during zooming can bemade small. Hence, the refractive power variable element can easily becontrolled.

Exemplified Embodiment 2

Exemplified embodiment 2 to be described below corresponds to the zoomlens according to the above-described second embodiment.

More specifically, the focal lengths, principal points, and principalpoint intervals of the respective groups, the group intervals, the focallength of the entire system, and the total length at object distance T=∞of the zoom lens are shown in Table 3. The focal lengths, principalpoints, and principal point intervals of the second lens group servingas a refractive power variable element at the short and long focallength ends at object distance T=250 mm are shown in Table 4. The objectdistance indicates the distance from the object to the surface apex ofthe zoom lens closest to the object. For HF, HR, and HD in the tables,the direction from the object to the image is defined as positive. TABLE3 (Short Focal Length End: W) T = ∞ First Group P1 (W) = −0.111 HF1 (W)= −1.062 HR1 (W) = 1.030 H01 (W) = 0.937 D1 (W) = 6.552 Second Group P2(W) = 0.171 HF2 (W) = 2.538 HR2 (W) = 4.020 HD2 (W) = 3.886 D2 (W) =0.997 Third Group P3 (W) = 0.098 HF3 (W) = −0.730 HR3 (W) = 0.626 HD3(W) = 0.652 D3 (W) = 2.378 Overall System f (W) = 4.519 L (W) = 20.332(Intermediate Focal Length End: M) T = ∞ First Group P1 (M) = −0.111 HF1(M) = −1.062 HR1 (M) = 1.030 HD1 (M) = 0.937 D1 (M) = 4.027 Second GroupP2 (M) = 0.167 HF2 (M) = 2.643 HR2 (M) = 4.082 HD2 (M) = 3.930 D2 (M) =3.522 Third Group P3 (M) = 0.098 HF3 (M) = −0.730 HR3 (M) = 0.626 HD3(M) = 0.652 D3 (M) = 2.378 Overall System f (M) = 6.999 L (M) = 20.332(Long Focal Length End: T) T = ∞ First Group P1 (T) = −0.111 HF1 (T) =−1.062 HR1 (T) = 1.030 HD1 (T) = 0.937 D1 (T) = 1.119 Second Group P2(T) = 0.179 HF2 (T) = 2.353 HR2 (T) = 3.910 HD2 (T) = 3.810 D2 (T) =6.430 Third Group P3 (T) = 0.098 HF3 (T) = −0.730 HR3 (T) = 0.626 HD3(T) = 0.652 D3 (T) = 2.378 Overall System f (T) = 11.060 L (T) = 20.332

TABLE 4 (Short Focal Length End: W)   T = 250 mm Second Group P2(W) =0.173 HF2(W) = 2.499 HR2(W) = 3.997 HD2(W) = 3.869 (Long Focal LengthEnd: T)   T = 250 mm Second Group P2(T) = 0.182 HF2(T) = 2.280 HR2(T) =3.868 HD2(T) = 3.780

As shown in Table 3, when the focal length is changed from the shortfocal length end to the long focal length end, and the refractive powerof the second lens group G2 is changed simultaneously, compensation tocorrect focus movement caused by zooming is executed while contributingto zoom. In addition, as shown in Table 4, focusing can also be executedby changing the refractive power of the refractive power variableelement as the object distance changes. For this reason, lens groupsother than the second lens group serving as an optical element grouphaving a zooming function can be fixed. Hence, a zoom lens which has asmall number of drive lens groups and a simple moving mechanism whilesuppressing the moving amount of the moving lens group small can beimplemented.

When the refractive power of the refractive power variable element hasan extremum during zooming to change the focal length from the shortfocal length end to the long focal length end, the change in refractivepower of the refractive power variable element during zooming be madesmall. Hence, the refractive power variable element can easily becontrolled.

Hereinafter, third and fourth embodiments, and exemplified embodiments 3and 4 in relation to the third and fourth embodiments are explained. Inthe third and fourth embodiments, a liquid optical element is used as arefractive power variable element.

FIGS. 5A to 5C are sectional views which show a zoom lens in a firstembodiment of the present invention, and among which FIG. 5A shows ashort focal distance end condition, FIG. 5B shows an intermediateposition, and FIG. 5C shows a long focal distance end condition. In theconfiguration of the first embodiment, the zoom lens has lens groups G1to G3 for focusing an object image on an image pick-up element CCD. Thefirst lens group G1 is composed of a negative first lens L1 and a liquidoptical element QL which are fixed to a lens frame which is not shown.The second lens group G2 is composed of a diaphragm S, a positive secondlens L2, a positive third lens L3 and a negative fourth lens L4, whichare moved integrally in an optical direction by a drive source which isnot shown. The third lens group G3 is composed of a positive fifth lensL5 which is fixed to a lens frame which is not shown.

FIG. 6 is a schematic view which shows a configuration of the liquidoptical element QL and a drive part. There are shown the liquid opticalelement QL in this embodiment, and a lower container 40 made of anon-conductive material. A first recess 41 is formed in a peripheralpart of a bottom surface (right inner surface as viewed in FIG. 6) ofthe lower container 40, and a second recess 42 for holding a firstsealing plate 2 is formed on the inner diameter side (center side) ofthe first recess 42. The first sealing plate (a liquid sealing member) 2is made of transparent acryl resin or glass.

A second electrode ring 43 is provided at the entire inner periphery ofa peripheral wall part of the lower container 40, and an insulationlayer 44 made of acryl resin or the like, for covering an electrode endsurface 43 a is formed on and made into close contact with the outersurface of the second electrode ring 43.

It is noted here that the peripheral wall part of the lower container 40is inclined so as to be near to the optical axis X on the right end sidethan on the left end side as viewed in the figure. Thus, the firstelectrode 43 and the insulation layer 44 are both also inclined withrespect to the optical axis X.

Further, the thickness of the insulation layer 44 is graduallyincreased, leftward as viewed in FIG. 6. Further, a water repellantlayer 11 coated thereover with a water repellent agent is formedunderneath the entire inner periphery of the insulation layer 44. Stillfurther, a hydrophilic layer 12 coated thereover with a hydrophilicagent is formed on the left side of the entire inner periphery of theinsulation layer 44.

There is shown an upper container 50 made of a nonconductive material,which holds a second sealing plate (a liquid sealing member) 6 made ofacryl resin or glass, on the inner diameter side thereof. Further, asheet-like first electrode ring 51 is formed on and made into closecontact with the left end surface of a peripheral part of the uppercontainer 50.

An insulation layer 52 is formed on and made into close contact with theouter surface of the first electrode ring 51. The insulation layer 52 isformed so as to cover only the outer edge side of the first electrodering 51 in order to obtain an exposed part 51 a which is made into closecontact with a first liquid 21 (which will be explainer later) so as toapply a voltage thereto.

Further, the peripheral wall part of the lower container 40 and theupper container are sealed to each other in a liquid-tight manner so asto form a container as a housing having a liquid chamber with apredetermined volume, which is defined by the lower container 40, theupper container 50 and the first and second sealing plates 2, 6.

This container has an axially symmetric shape with respect to theX-axis. Further, the liquid chamber is filled therein with two kinds ofliquids as explained hereinafter.

At first, in such a condition that the optical axis X of the lowercontainer 40 attached thereto with the first sealing plate 2 is directedvertically, a second liquid 22 is dripped onto the upper surface of thefirst sealing plate 2 serving as a liquid bottom surface, and the bottomsurface of the outer peripheral side of the lower container 40 (namely,these surface correspond to surfaces opposed to the interface) by aquantity with which the liquid column height of the second liquid 22becomes an intermediate height of the water repellent membrane 11 in theperipheral wall part.

As the second liquid 22, silicone oil which is colorless andtransparent, having a specific weight of 1.06 and a refractive index of1.45 at a room temperature, is used. Then, the remaining space in theliquid chamber is filled with the first liquid 21. The first liquid 21(a liquid having a conductivity or a polarity) is an electrolyticsolution in which water and alcohol are mixed at a predetermined rateand is added thereto with a predetermined quantity of sodium chloride,so as to have a specific weight of 1.06 and a refractive index of 1.35at a room temperature.

Namely, as the first and second liquids 21, 22, two kinds of liquidswhich have an equal specific weight but different refractive indices andwhich are not mixed with each other (which are insoluble) are selected.Both liquids define therebetween the interface 24, and are presentindependent from each other, without being mixed with each other.

The shape of the interface 24 is determined by a point at which threekinds of substances, that is, the inner surface of the liquid chamber(container), the first liquid 21 and the second liquid 22, cross oneanother, or a balance among three interfacial tensions exerted to theouter edge part of the interface 24. Thereafter, the upper container 50attached thereto with the second sealing plate 6 is fitted to the lowercontainer 40, and thus, the two kinds of liquids are enclosed.

There is shown a power feed circuit 31 connected to the first electrodering 51 and the second electrode ring 43.

Two amplifiers (which is not shown) in the power feed circuit 31 areconnected respectively to terminals 51 b, 43 b which are led out fromthe first electrode ring 25 and the second electrode ring 3 in adirection orthogonal to the optical axis along the right end surface ofthe upper container 50.

With the above-mentioned configuration, when a voltage is applied to thefirst liquid 21 by way of the first electrode ring 51 and the secondelectrode ring 43, the interface 24 is deformed due to the so-calledelectrowetting effect.

Next, explanation will be hereinafter made of the deformation of theinterface 24 in the liquid optical element QL, and optical functionsexhibited by the deformation.

At first, in the case of no application of a voltage to the first liquid21, as shown in FIG. 2, the shape of the interface 24 is determined byan interfacial tension between both first and second liquids 21, 22, aninterfacial tension between the first liquid 21 and the water repellentmembrane 11 or the hydrophilic membrane 12 on the insulation layer 44,an interfacial tension between the second liquid 22 and the waterrepellent membrane 11 or the hydrophilic membrane 12 on the insulationlayer 44, and a volume of the second liquid 22.

Meanwhile, when a voltage is applied from the power supply circuit 31 tothe first liquid 21, the interfacial tension between the first liquid 21and the hydrophilic membrane 12 is decreased due to the electrowettingeffect, and accordingly, the first liquid 21 enters onto the waterrepellent membrane 11, overriding the boundary between the hydrophilicmembrane 12 and the water repellent membrane 11. As a result, the heightof the second liquid 22 as measured on the optical axis is increased.

Thus, with the application of a voltage to the first liquid 21 throughthe first and second electrode rings 51, 43, the balance of theinterfacial tension between the two kinds of the liquids varies, andaccordingly, the shape of the interface 24 between both liquids 21, 22is changed. Thus, through the voltage control by the power supplycircuit 31, it is possible to provide an optical element which canoptionally change the shape of the interface 24.

Further, since the first and second liquids 21, 22 have differentrefractive indices, an optical power (1/f where f is a focal distance)is applied so as to serve as a lens, that is, the liquid optical elementQL changes its focal distance due to a variation in the shape of theinterface 24.

Explanation will be made of the operation of the zoom lens in the firstembodiment, in the case of the zoom drive from the short focal distanceend to the long focal distance end, as shown in FIGS. 5A to 5C, thesecond lens group G2 is moved in the direction of the optical axis fromthe position shown in FIG. 5A and through the position shown in FIG. 5B,and is then moved to the position shown in FIG. 5C, and in the case ofthe zoom drive from the long focal distance end to the short focaldistance end, the operation is carried out in the reverse order. It isnoted that in the case of a convention zoom lens, the first lend groupG1 has to be moved in the direction of the optical axis in associationwith the movement of the second lens group G2 in the direction of theoptical axis, and accordingly, it is necessary to provide a cammechanism for driving the first lens group G1 in the optical directionin order to effect the compensation function, resulting in a complicatedconfiguration and in a large-sized image pick-up device in which thezoom lens is installed.

On the contrary, with the zoom lens in this embodiment, when the zoomdrive is carried out in the zoom lens as shown in FIGS. 5A to 5C, thepower supply circuit 31 computes a required compensation value from azoom signal (or refers to a table), and applies a predetermined voltageto the liquid optical element QL. With this control, the liquid opticalelement QL optionally changes its optical power so as to materialize acompensation function. Thus, it is possible to eliminate the necessityof a mechanism for moving the first lens group G1 in the direction ofthe optical axis, thereby it is possible to aim at simplifying theconfiguration of the zoom lens and at making the zoom lens compact. Itis preferable to change the optical power, multi-stepwise, and is morepreferable to change the optical power, continuously.

Further, in a conventional zoom lens in which the displacement of thefirst lens group in the direction of the optical axis corresponds tothat of the second lens group in the direction of the optical axis at aratio of 1:1 due to a shape of a cam, since the object distance isvariable in actual image pick-up, the third lens group G3 should bemoved in the direction of the optical axis in order to adjust a focus ona light receiving surface of an image pick-up element CCD or the like inassociation with the movement of the first and second lens groups G1, G2in order to effect a focus function. In this case, it is necessary toadd a separate drive mechanism for the third lens group G3, resulting ina complicated configuration, and in a large sized zoom lens.

On the contrary, in the first embodiment, the power supply circuit 31changes the shape of the liquid optical element QL in accordance with asignal from the image pick-up element CCD or a measured distance signalfrom a distance measuring equipment which is not shown, and a zoomsignal (a displacement of the second lens group G2 in the direction ofthe optical axis) in order to simultaneously effect the compensationfunction and the focus function (further, it may execute a part of thezooming function). In this case, it is possible to offer such atechnical effect that the movement of the third lens group G3 in thedirection of the optical axis is not required.

FIGS. 7A to 7C are sectional views which show a zoom lens in a secondembodiment of the present invention, and among which FIG. 7A shows ashort focal distance end condition, FIG. 7B is an intermediate conditionand FIG. 7C is a long focal distance condition.

In this second embodiment, the zoom lens has lens groups G1 to G3 forfocusing an object image on an image pick-up element CCD. The first lensgroup G1 is composed of a negative first lens L1 and a positive secondlens L2, and is fixed to a lens frame which is not shown. The secondlens group G2 is composed of a diaphragm S, a liquid optical element QL,a positive third lens L3 and a negative fourth lens L4, which are movedintegral with one another in the direction of the optical axis. Thethird lens group G3 is composed of a positive fifth lens L5 which isfixed to a lens frame which is not shown. It is noted that the basicconfiguration of the liquid optical element QL used in this embodimentis the same as that shown in FIG. 6, and accordingly, the explanationthereof will be omitted.

Explanation will be made of the operation of the zoom lens in the secondembodiment, in the case of zoom drive from the short focal distance endto the long focal distance end, as shown in FIG. 6, the second lensgroup G2 is moved in the direction of the optical axis from the positionshown in FIG. 7A and through the position shown in FIG. 7B, and is movedto the position shown in FIG. 7C. The zoom drive from the long focaldistance end to the short focal distance end, the operation is made inthe reverse order.

In the second embodiment, when the zoom operation of the zoom lens shownin FIGS. 5A to 5C is executed, the power supply circuit for the liquidoptical element QL computes a required compensation value from a zoomsignal (or refers to a table), and applies a predetermined voltage tothe liquid optical element QL. Through such control, the liquid opticalelement QL optionally changes optical power so as to effect acompensation function. Thus, it is possible to eliminate the necessityof a mechanism for moving the first lens group G1 in the direction ofthe optical axis, thereby it is possible to aim at simplifying theconfiguration of the zoom lens and making the zoom lens compact. It ispreferable to change the optical power multi-stepwise, and it is morepreferable to change the optical power, continuously.

Further, in the second embodiment, the power supply circuit for theliquid optical element QL can change the shape of the liquid opticalelement QL in accordance with a signal from the image pick-up elementCCD or a measured distance signal from a distance measuring equipmentand a zoom signal (or a displacement of the second lens group G2 in thedirection of the optical axis) in order to simultaneously effect thecompensation function and the focus function (further, it may effect apart of the zooming function). In this case, it is possible to offersuch a technical effect that the movement of the third lens group G3 inthe direction of the optical axis is not necessary.

By allowing the liquid optical element QL to have a complete zoomingfunction in the first and second embodiments, all lens groups can befixed in the direction of the optical axis. Thereby, it is possible toprovide a zoom lens with no drive mechanism for lens groups.

FIG. 10 is a perspective view which shows a zoom lens unit ZU in whichthe zoom lens in the above-mentioned embodiments and a drive meanstherefor are incorporated, integral with each other. Referring to FIG.10, walls W1, W2 are extended upward from opposite ends of a base B. Aguide shaft GS is extended so to couple the walls W1, W2 (which areshown being cutout) in the vicinity of the upper ends thereof. Further,the walls W1, W2 are formed therein with opening holes HL, respectively,through which a light beam passes.

The first lens group G1 is held at its outer periphery by a lens holderHD1, and is mounted so as to cover the opening hole HL in the wall W1.It is preferable to restrain a shift or a tilt with respect to areference axis as possible as it can with the use of an autocollimatoror the like during assembly of the first lens group G1.

Meanwhile, the second lens group G2 serving as an optical element groupfor zooming, is held at its outer periphery by a lens holder HD2. Thelens holder HD2 serving as a movable member comprises an engaging partHDa engaged with the guide shaft GS, and a coupling part HDb forreceiving a drive force.

The coupling part HDb is formed therein with a groove which makescontact with a drive shaft DS, and is attached at its upper surface witha leaf spring SG. The drive shaft DS serving as a drive member is heldbetween the coupling part HDb and the leaf spring SG, and isappropriately pressed by an urging force of the leaf spring SG. A gap isdefined at one end of the drive shaft DS on the wall W1 side, and theother end part of the drive shaft DS is extended through the wall W2 andis coupled to a piezoelectric actuator PZ serving as anelectromechanical conversion element. The piezoelectric actuator PZ hasa fixing part Bh which is fixed to the base B outside of the wall W2 byan adhesive or the like.

The third lens group G3 is fitted in the opening hole HL in the wall W2.Further, adjacent to the third lens group G3, a solid image pick-upelement CCD is attached to the wall W2. The relationship among the firstlens group G1, the second lens group L2 and the third lens group L3 inthe direction of the optical axis is as shown in FIGS. 5A to 5C andFIGS. 7A to 7C.

An external drive circuit (which is not shown) is provided on the baseB, and is adapted to receive a signal from an encoder which is not shown(which is a position detecting means composed of, for example, magneticinformation arranged on the guide shaft GS and a reading head mounted onthe engaging part HDa) for magnetically detecting a displacement of theengaging part HDa, and to apply the drive voltage to the piezoelectricactuator PZ by way of wiring H in order to drive and control thepiezoelectric actuator PZ. The drive means is composed of piezoelectricactuator PZ, the drive shaft DS, the coupling part HDb and the leafspring SG. It is noted that the drive circuit arranged on the base B maybe connected by wiring.

The piezoelectric actuator PZ is composed of piezoelectric ceramicswhich are made of PZT (lead zironate titanate) and which are laminatedone upon another. The piezoelectric ceramic has, in crystal lattice, apositive electric charge and a negative electric charge whosegravitation centers are not coincident with each other, and is itselfpolarized. Accordingly, when the drive voltage is applied to thepiezoelectric ceramic in its polarizing direction, it is elongated.However, the degree of distortion of the ceramic in this direction isextremely small, and accordingly, it is difficult to drive a member tobe driven by this small degree of the distortion. Thus, as shown in FIG.11, there are provided a lamination type piezoelectric actuator PZhaving such a configuration that a plurality of piezoelectric ceramicsPE are laminated one upon another and electrodes C are interposedtherebetween and are connected in parallel with one another. In the zoomlens of the present invention, this lamination type piezoelectricactuator PZ is used as a drive source.

Next, explanation will be made of a method of driving the second lensgroup G2 by the zoom lens unit ZU. In general, the lamination typepiezoelectric actuator PZ exhibits a small displacement upon applicationof the drive voltage, but produces a large force with a sharp response.Accordingly, as shown in FIG. 12A, by applying voltage pulses eachhaving a saw-like waveform having a steep leading edge but a gentletailing edge to the lamination type piezoelectric actuator PZ, theactuator PZ abruptly expands at the leading edge of the pulse but slowlycontracts at a trailing edge thereof. Thus, upon extension of thepiezoelectric actuator PZ, the drive shaft DS is pushed inward in FIG.10 (toward the wall W1 side) by an impact force thereby, but thecoupling part HDb of the lens holder HD2 which holds the second lensgroup G2 and the leaf spring SG do not move together with the driveshaft DS due to their inertia but slip on the drive shaft DS so as tostay in a present position (although slight movement is possiblycaused). Meanwhile, since the drive shaft DS moves back at the trailingedge of the pulse, slowly, in comparison with the leading edge thereof,the coupling part HDb and the leaf spring SG do not slip on the driveshaft DS, but move integral with the drive shaft DS toward the near side(toward the wall W2) in FIG. 10. That is, by applying pulses having afrequency set in a range from several hundred to several ten thousandHz, the lens holder HD2 can be moved at a desired speed. As clearlyunderstood from the above, if a pulse having a gentle leading edge but asteep trailing edge as shown in FIG. 12B is applied, the lens holder HD2can be moved in the reverse direction. In particular, if the guide shaftGS is straight, the lens holder HD2 is precisely moved in the directionof the optical axis, thereby it is possible to effectively restraindeterioration of aberration in comparison with such a configuration thatdeviation of the optical axis occurs.

As described above, it becomes possible to change the speeds ofextensions and contractions of the zoom lens in accordance with theshape of pulse applied to the piezoelectric actuator PZ as theelectromechanical conversion element.

In addition, due to repetitions of extension and contraction of thepiezoelectric actuator PZ, the movable member (lens holder HD2) can becontinuously moved in one direction. That is, with the use of the drivemeans according to the present invention, having a high responsiveness,the optical element groups which are moved upon zooming can be moved ata high speed, and can be also moved by a slight displacement. Further,in such a case that the optical element groups which are moved uponzooming, are held in position, when the supply of an electric power tothe piezoelectric actuator PZ is interrupted, they are held by afriction force between the movable member and the drive member, therebyit is possible to aim at saving energy. In addition, it can offer suchan advantage that the configuration of the drive means can besimplified, and can be at a low cost.

Explanation will be made of two exemplified embodiments of the zoom lensaccording to the present invention. The following marks will be used inthe exemplified embodiments.

-   -   f: Focal distance of an entire image pick-up lens system;    -   F: F number    -   T: Object distance    -   R: Radius of curvature    -   D: On-axis inter-surface space    -   Nd: Refractive Index of lens material with respect to d-ray    -   νd: Abbe's Number of lens material

The shape of an aspheric surface in each of the exemplified embodimentscan be exhibited by the following formula (1) where the vertex of thespherical surface is set an original point and X-axis is set in thedirection of the optical axis: $\begin{matrix}{X = {\frac{h^{2}/R}{1 + \sqrt{1 - {\left( {1 + K} \right){h^{2}/R^{2}}}}} + {\sum{A_{i}h^{i}}}}} & (1)\end{matrix}$where

-   -   h: is a height in a direction perpendicular to the optical axis    -   Ai: i-order aspheric coefficient    -   R: radius of curvature    -   K: Conical Constant

Exemplified Embodiment 3

The exemplified embodiment 3 which will be explained hereinafterconcerns the zoom lens in the third embodiment. Data of the zoom lens inthis exemplified embodiment 3 is listed in table 5, and radii R5 ofcurvature at a short focal distance end, an intermediate focal distanceand a long focal distance end with an object distance T=∞, inter-surfacespaces D4, D5 and F as F-number, a focal distance f of an entire imagepick-up lens system and a viewing angle 2ω are listed in table 6.Further, aspheric data are listed in table 7, and further, radii R5 ofcurvature at a short focal distance end and a long focal distance endwith an object distance T=250 mm, and inter-surface spaces D4, D5 arelisted in table 8. Further, FIGS. 8A and 8C show aberration charts at ashort focal distance (FIG. 8A), at an intermediate focal distance (FIG.8B) and at a long focal distance (FIG. 8C) with an object distance T=°°in the exemplified embodiment 3. It is noted here that the objectdistance is from the object to the vertex of the most object sidesurface of the zoom lens. It is noted that a power number of 10 (forexample, 2.5×10⁻⁰³ is exhibited by E (for example, 2.0E-03). TABLE 5 f =4.5 mm˜7.3 mm˜11.2 mm F = 3.0˜4.2˜5.2 2ω = 66°˜42°˜28° Surface No. R(mm) D (mm) Nd 1 −29.924 0.80 1.53180 2 4.382 2.07 3 12.064 1.39 1.607004 ∞ D4(variable) 1.35000 5 R5(variable) D5(variable) 1.45000 6 ∞ 0.801.53180 7 104.888 D7(variable) Diaphragm ∞ 0.40 8 4.870 1.52 1.58913 9−12.045 0.22 10  7.844 1.50 1.53180 11  −34.269 1.28 1.60700 12  2.606D12(variable) 13  5.725 3.27 1.53180 14  58.204 2.20 15  ∞ 0.50 1.5163316  ∞

TABLE 6 T = ∞ Short focal Intermediate Long focal distance end focaldistance distance end f 4.5 7.3 11.2 F 3.0 4.2 5.2 2ω 66° 42° 28° R5 ∞−15.00 ∞ D4 0.50 0.73 0.50 D5 0.75 0.52 0.75 D7 8.85 4.38 0.55 D12 1.505.97 9.80

TABLE 7 Aspheric Coefficient 1^(st) Surface: A4 =   7.03770E−04 A6 =  2.16940E−06 A8 = −9.72750E−07 A10 =   1.34040E−08 2^(nd) Surface: A4 =−1.94030E−03 A6 =   1.40750E−04 A8 = −9.95290E−06 3^(rd) Surface: K =  6.46670E−01 A4 = −1.39680E−03 A6 =   5.41890E−05 A8 = −4.77660E−06 A10=   3.46040E−07 7^(th) Surface: A4 = −9.79050E−04 A6 =   2.99920E−05 A8= −3.73820E−07 A10 =   2.83750E−07 10^(th) Surface: K = −3.88660E−00 A4= −2.98360E−03 A6 = −3.04150E−05 A8 = −3.42510E−05 A10 =   1.76260E−0612^(th) Surface: K =   1.86790E−01 A4 = −6.44580E−03 A6 = −1.14390E−03A8 =   1.77060E−04 A10 = −6.65490E−05 13^(th) Surface: K =   7.17560E−01A4 = −1.15060E−03 A6 =   4.71500E−05 A8 =   6.76360E−07 A10 =−2.22870E−07 14^(th) Surface: A4 =   2.20080E−04 A6 = −1.03240E−04 A8 =  3.91670E−05 A10 = −2.85110E−06 A12 =   6.65910E−08

TABLE 8 T = 250 mm Short focal Long focal distance end distance end R548.40 48.40 D4 0.50 0.50 D5 0.75 0.75

As listed in table 6, by changing the focal distance from the shortfocal distance end to the long focal distance end and by changing theradius of curvature of the interface in the liquid optical element QL,compensation for correcting a focus movement caused by zooming can becarried out, and as listed in table 8, by changing the radius ofcurvature of the interface in association with a variation in objectdistance, focusing can be made. Thus, the lens groups other than thesecond lens group serving as a lens group for zooming can be fixed tolens frames, it is possible to provide a zoom lens having a simplemechanism with a less number of driven lenses. Further, with such aconfiguration in which the radius of curvature of the interface has anextremum while the focal distance is changed from the short focaldistance end to the long focal distance end, a variation in therefractive power of the liquid optical element QL can be less, therebyit is possible to simplify the control of the liquid optical element QL.

Further, in the case of no application of a voltage to the liquidoptical element QL, or in the case of application of a lower voltage,the shape of the interface is set so as to obtain a refractive powerwhich is frequently used upon image pick-up, thereby it is possible toprovide a zoom lens with less power consumption. Thus, it is morepreferable.

Exemplified Embodiment 4

The exemplified embodiment 4 which will be explained hereinbelowconcerns the zoom lens in the fourth embodiment. Data of the zoom lensin this exemplified embodiment 4 is listed in table 9, and radii R5 ofcurvature at a short focal distance end, an intermediate focal distanceand a long focal distance end with an object distance T=∞, inter-surfacespaces D4, D5 and F as F-number, a focal distance f of an entire imagepick-up lens system and a viewing angle 2ω are listed in table 10.Further, aspheric data are listed in table 11, and further, radii R5 ofcurvature at a short focal distance end, an intermediate focal distanceand a long focal distance end with an object distance T=250 mm, andinter-surface spaces D4, D5 are listed in table 12.

Further, FIGS. 9A and 9C show aberration charts at a short focaldistance (FIG. 9A), at an intermediate focal distance (FIG. 9B) and at along focal distance (FIG. 9C) with an object distance T=∞ in theexemplified embodiment 4. It is noted here that the object distance isfrom the object to the vertex of the most object side surface of thezoom lens. It is noted that a power number of 10 (for example,2.5×10<sup>−03</SUP> is exhibited by E (for example, 2.0E-03). TABLE 9 f= 4.5 mm˜7.0 mm˜11.1 mm F = 3.0˜3.9˜4.9 2ω = 66°˜43°˜28° Surface No. R(mm) D (mm) Nd νd 1 −27.144 0.80 1.53180 56.0 2 5.359 0.94 3 5.239 1.291.60700 27.0 4 5.566 D4(variable) Diaphragm ∞ 0.40 5 3.577 1.40 1.5891361.2 6 ∞ D6(variable) 1.35000 59.0 7 R7(variable) D7(variable) 1.4500044.0 8 ∞ 0.50 1.51633 64.1 9 ∞ 0.20 10  4.231 1.22 1.53180 56.0 11 54.916 0.80 1.60700 27.0 12  2.704 D12(variable) 13  11.347 2.01 1.5318056.0 14  −9.726 2.05 15  ∞ 0.50 1.51633 64.1 16  ∞

TABLE 10 T = ∞ Short focal Intermediate Long focal distance end focaldistance distance end f 4.5 7.0 11.1 F 3.0 3.9 4.9 2ω 66° 43° 28° R7−33.00 −14.30 22.00 D4 6.15 3.63 0.72 D6 0.58 0.61 0.51 D7 0.67 0.640.74 D12 1.00 3.52 6.43

TABLE 11 Aspheric Coefficient 1^(st) Surface: A4 =   1.40080E−02 A6 =−1.44900E−03 A8 =   6.18690E−05 A10 = −9.29280E−07 2^(nd) Surface: A4 =  1.70690E−02 A6 =   1.06930E−03 A8 = −2,13460E−04 3^(rd) Surface: K =−1.55790E−01 A4 =   7.24870E−03 A6 =   1.80440E−04 A8 =   2.97720E−05A10 = −1.51380E−05 4^(th) Surface: A4 = −9.03080E−03 A6 =   2.27360E−03A8 = −4.15700E−04 A10 =   2.06310E−05 10^(th) Surface: K = −2.72330E−00A4 = −4.87790E−03 A6 = −1.14690E−03 A8 = −1.63160E−04 A10 = −1.01850E−0512^(th) Surface: K =   1.47700E−02 A4 = −4.62840E−03 A6 = −1.36410E−03A8 = −2.92520E−04 A10 = −4.42360E−05 13^(th) Surface: K =   5.15310E−00A4 = −3.00180E−03 A6 =   4.48110E−04 A8 = −2.06570E−05 A10 =  6.95950E−07 14^(th) Surface: A4 = −3.03100E−03 A6 =   4.03150E−04 A8 =−1.22050E−05 A10 =   7.67460E−07

TABLE 12 T = 250 mm Short focal Long focal distance end distance end R7−68.40 12.95 D6 0.58 0.51 D7 0.67 0.74

As listed in table 10, by changing the focal distance from the shortfocal distance end to the long focal distance end and by changing theradius of curvature of the interface in the liquid optical element QL,compensation for correcting a focus movement caused by zooming can becarried out while contributing to zoom, and as listed in table 12, bychanging the radius of curvature of the interface in association with avariation in object distance, focusing can be made. Thus, the lensgroups other than the second lens group serving as a lens group forzooming can be fixed to lens frames, it is possible to provide a zoomlens having a simple mechanism with a less number of driven lenses.Further, with such a configuration in which the radius of curvature ofthe interface has an extremum while the focal distance is changed fromthe short focal distance end to the long focal distance end, a variationin the refractive power of the liquid optical element QL can be less,thereby it is possible to simplify the control of the liquid opticalelement QL.

Further, in the case of no application of a voltage to the liquidoptical element QL, or in the case of application of a lower voltage,the shape of the interface is set so as to obtain a refractive powerwhich is frequently used upon image pick-up, thereby it is possible toprovide a zoom lens with less power consumption. Thus, it is morepreferable.

The embodiments of the present invention have been described above. Thepresent invention is not limited to the above embodiments, and variouschanges and modifications can appropriately be made. For example, thethird lens group G3 may be a refractive power variable element. The lensgroup may include only a single refractive power variable element or acombination of a normal lens and refractive power variable element. Thetype of the refractive power variable element is not particularlylimited. Any element which can change the refractive power by changingthe shape of the lens surface or the refractive index of the materialcan be used. The zoom lens of the present invention is preferablymounted in an image sensing apparatus such as a compact digital stillcamera or a portable terminal such as a cellular phone or PDA. However,the present invention is not limited to this.

1. A zoom lens in which a plurality of optical element groups includingat least an optical element group which moves in zooming are arranged ina lens system, comprising: a refractive power variable element of atransmission type which is mounted in at least one of the plurality ofoptical element groups, the refractive power variable element having acompensation function to correct focus movement caused by zooming and afocus function to correct focus movement caused by a variation ininter-object distance.
 2. A zoom lens in which a plurality of opticalelement groups including at least an optical element group which movesin zooming are arranged in a lens system, comprising: at least arefractive power variable element of a transmission type provided in theplurality of optical element groups; an electromechanical conversionelement which is extendible/contractible by applying thereto a drivevoltage in the form of predetermined pulses; a drive member fixed to oneend of the electromechanical conversion element; a movable membercoupled to the optical element group and movably mounted on the drivemember; and a drive means for moving the movable member throughrepetitions of extension and contraction of the electromechanicalconversion element at different speeds in directions of extension andcontraction which is caused by applying the drive voltage in the form ofthe predetermined pulses to the electromechanical conversion element. 3.A zoom lens according to claim 1, wherein a refractive power of theoptical element group including the refractive power variable element ofa transmission type has an extremum during zooming.
 4. A zoom lensaccording to claim 1, wherein the refractive power is changed bychanging a radius of curvature of an optical surface at which therefractive power variable element contacts air.
 5. A zoom lens accordingto claim 1, wherein the refractive power is changed by changing arefractive index of an optical material making the optical element.
 6. Azoom lens according to claim 1, wherein only one optical element groupmoves in zooming.
 7. A zoom lens according to claim 1, wherein aposition of the optical element group including the refractive powervariable element is fixed in a direction of an optical axis.
 8. A zoomlens according to claim 1, the zoom lens comprises a refractive powervariable element mounted in an optical element group which moves inzooming, the refractive power variable element having a compensationfunction to correct focus movement caused by zooming, a focus functionto correct focus movement caused by a variation in inter-objectdistance, and a zooming function.
 9. A lens according to claim 1,wherein the optical element group including the refractive powervariable element includes a diaphragm.
 10. A zoom lens according toclaim 1, wherein the refractive power variable element of a transmissiontype comprises a liquid optical element including a first liquid havinga conductivity or a polarity and a second liquid which is not mixed withthe first liquid, the first liquid and the second liquid being enclosedin a container fluid-tight so as to define an interface therebetweenhaving a predetermined shape, the liquid optical element being arrangedsuch that a refractive power thereof is adjusted by changing a curvatureof the interface.
 11. A zoom lens according to claim 10, wherein theliquid optical element is arranged in an optical element group whichincludes a diaphragm.
 12. A zoom lens according to claim 10, wherein inthe case of an optical element group which does not include a diaphragmbut the liquid optical element, the liquid optical element is arrangedat a position neared to the diaphragm.
 13. A zoom lens according toclaim 10, wherein one of the optical element groups is moved uponzooming.
 14. A zoom lens according claim 10, wherein the optical elementgroup including the liquid optical element is fixed in the direction ofthe optical axis, and the optical element group including the liquidoptical element has a compensation function for correcting a focusmovement caused by zooming and a focus function for correcting a focusmovement caused by a variation in object distance.
 15. A zoom lensaccording to claim 2, wherein each of the pluses has a saw-toothedshape.
 16. A camera, comprises: a zoom lens having at least an opticalelement group provided in a plurality of optical element groups arrangedin a lens system, the optical element group being made to move inzooming, and at least a refractive power variable element of atransmission type having a compensation function to correct focusmovement caused by zooming and a focus function to correct focusmovement caused by a variation in inter-object distance.